Editing Carrying capacity (section)

== Recent warnings that humanity may have exceeded Earth's carrying capacity ==
Between 1900 and 2020, Earth's human population increased from 1.6 billion to 7.8 billion (a 390% increase).<ref>{{Cite web |date=2022 |title=World Population Prospects - Population Division - United Nations |url=https://population.un.org/wpp/ |access-date= |website=population.un.org |publisher=UN Department of Economic and Social Affairs}}</ref> These successes greatly increased human resource demands, generating significant [[environmental degradation]].<ref name=":0">Reid, W. V., et al. (2005). ''The millennium ecosystem assessment: Ecosystems and human well-being.'' Washington, DC: Island Press.</ref>

=== Millennium ecosystem assessment ===
The Millennium Ecosystem Assessment (MEA) of 2005 was a massive, collaborative effort to assess the state of Earth's ecosystems, involving more than 1,300 experts worldwide.<ref name=":0" /> Their first two of four main findings were the following. The first finding is:<blockquote>Over the past 50 years, humans have changed ecosystems more rapidly and extensively than in any comparable period of time in human history, largely to meet rapidly growing demands for food, fresh water, timber, fiber, and fuel. This has resulted in a substantial and largely irreversible loss in the diversity of life on Earth.<ref name=":1">Reid, W. V., et al. (2005). ''The millennium ecosystem assessment: Ecosystems and human well-being.'' Washington, DC: Ecosystems and Human Well-Being: A Synthesis, p. 1.</ref></blockquote>The second of the four main findings is:<blockquote>The changes that have been made to ecosystems have contributed to substantial net gains in human well-being and economic development, but these gains have been achieved at growing costs in the form of the degradation of many ecosystem services, increased risks of nonlinear changes, and the exacerbation of poverty for some groups of people. These problems, unless addressed, will substantially diminish the benefits that future generations obtain from ecosystems.<ref name=":1" /></blockquote>According to the MEA, these unprecedented environmental changes threaten to reduce the Earth's long-term human carrying capacity. “The degradation of ecosystem services could grow significantly worse during the first half of this [21st] century,” they write, serving as a barrier to improving the lives of poor people around the world.<ref name=":1" />

=== Ecological footprint accounting ===
[[Ecological footprint]] accounting measures the demands people make on nature and compares them to available supplies, for both individual countries and the world as a whole.<ref name=":2">Mathis Wackernagel and Bert Beyers, 2019. ''Ecological Footprint: Managing Our Biocapacity Budget.'' New Society Publishers.</ref> Developed originally by [[Mathis Wackernagel]] and [[William E. Rees|William Rees]], it has been refined and applied in a variety of contexts over the years by [[Global Footprint Network]] (GFN). On the demand side, the ecological footprint measures how fast a population uses resources and generates wastes, with a focus on five main areas: carbon emissions (or [[carbon footprint]]); land devoted to direct settlement; timber and paper use; food and fiber use; and seafood consumption.<ref name=":3">{{Cite web |title=Global Footprint |url=https://www.footprintnetwork.org/our-work/ecological-footprint/ |website=Global Footprint Network}}</ref> It converts these into per capita or total hectares used. On the supply side, national or global [[biocapacity]] represents the productivity of ecological assets in a particular nation or the world as a whole; this includes “cropland, grazing land, forest land, fishing grounds, and built-up land.”<ref name=":3" /> Again the various metrics to capture biocapacity are translated into the single term of hectares of available land. As Global Footprint Network (GFN) states:<blockquote>Each city, state or nation’s Ecological Footprint can be compared to its biocapacity, or that of the world. If a population’s Ecological Footprint exceeds the region’s biocapacity, that region runs a biocapacity deficit. Its demand for the goods and services that its land and seas can provide—fruits and vegetables, meat, fish, wood, cotton for clothing, and carbon dioxide absorption—exceeds what the region’s ecosystems can regenerate. In more popular communications, this is called “an ecological deficit.” A region in ecological deficit meets demand by importing, liquidating its own ecological assets (such as overfishing), and/or emitting carbon dioxide into the atmosphere. If a region’s biocapacity exceeds its Ecological Footprint, it has a biocapacity reserve.<ref name=":3" /></blockquote>According to the GFN's calculations, humanity has been using resources and generating wastes in excess of sustainability since approximately 1970: currently humanity use Earth's resources at approximately 170% of capacity.<ref>{{Cite web |title=Footprint Data Platform |url=https://data.footprintnetwork.org |website=Global Footprint Network}}</ref><ref>{{Cite journal |title=Living Planet Report 2020: Bending the Curve of Biodiversity Loss |url=http://dx.doi.org/10.1163/9789004322714_cclc_2020-0074-0399 |access-date=2023-06-30 |website=Climate Change and Law Collection|doi=10.1163/9789004322714_cclc_2020-0074-0399 }}</ref> This implies that humanity is well over Earth's human carrying capacity for our current levels of affluence and technology use. According to Global Footprint Network:<blockquote>In 2024, [Earth Overshoot Day] fell on August 1. Earth Overshoot Day marks the date when humanity has exhausted nature’s budget for the year. For the rest of the year, we are maintaining our ecological deficit by drawing down local resource stocks and accumulating carbon dioxide in the atmosphere. We are operating in overshoot.<ref>{{Cite web |title=Earth Overshoot Day |url=https://www.footprintnetwork.org/our-work/earth-overshoot-day/ |website=Global Footprint Network}}</ref></blockquote>The concept of ‘[[ecological overshoot]]’ can be seen as equivalent to exceeding human carrying capacity.<ref>Catton, W. R. (1982). ''Overshoot: The ecological basis of revolutionary change''. University of Illinois Press.</ref><ref name=":2" /> According to the most recent calculations from Global Footprint Network, most of the world's residents live in countries in ecological overshoot (see the map on the right).  
[[File:Ecological_footprint.png|thumb|[https://data.footprintnetwork.org/?_ga=2.21888827.1692355221.1664332869-1465536352.1663440999#/ Nations living within their ecological means (shaded green) or in ecological overshoot] (shaded red) in 2022.]]This includes countries with dense populations (such as China, India, and the Philippines), countries with high per capita consumption and resource use (France, Germany, and Saudi Arabia), and countries with both high per capita consumption and large numbers of people (Japan, the United Kingdom, and the United States).<ref name=":3" />

=== Planetary boundaries framework ===
According to its developers, the planetary boundaries framework defines “a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system.”<ref name=":4" /> Human civilization has evolved in the relative stability of the [[Holocene epoch]]; thus crossing planetary boundaries for safe levels of atmospheric carbon, ocean acidity, or one of the other stated boundaries could send the global ecosystem spiraling into novel conditions that are less hospitable to life—possibly reducing global human carrying capacity. 

This framework, developed in an article published in 2009 in ''[[Nature (journal)|Nature]]''<ref>{{Cite journal |last1=Rockström |first1=Johan |last2=Steffen |first2=Will |last3=Noone |first3=Kevin |last4=Persson |first4=Åsa |last5=Chapin |first5=F. Stuart III |last6=Lambin |first6=Eric |last7=Lenton |first7=Timothy M. |last8=Scheffer |first8=Marten |last9=Folke |first9=Carl |last10=Schellnhuber |first10=Hans Joachim |last11=Nykvist |first11=Björn |last12=de Wit |first12=Cynthia A. |last13=Hughes |first13=Terry |last14=van der Leeuw |first14=Sander |last15=Rodhe |first15=Henning |date=2009 |title=Planetary Boundaries: Exploring the Safe Operating Space for Humanity |url=http://dx.doi.org/10.5751/es-03180-140232 |journal=Ecology and Society |volume=14 |issue=2 |doi=10.5751/es-03180-140232 |issn=1708-3087|hdl=10535/5421 |s2cid=15182169 |hdl-access=free }}</ref> and then updated in two articles published in 2015 in ''Science''<ref name=":4" /> and in 2018 in ''PNAS'',<ref name=":5">{{Cite journal |last1=Steffen |first1=Will |last2=Rockström |first2=Johan |last3=Richardson |first3=Katherine |last4=Lenton |first4=Timothy M. |last5=Folke |first5=Carl |last6=Liverman |first6=Diana |last7=Summerhayes |first7=Colin P. |last8=Barnosky |first8=Anthony D. |last9=Cornell |first9=Sarah E. |last10=Crucifix |first10=Michel |last11=Donges |first11=Jonathan F. |last12=Fetzer |first12=Ingo |last13=Lade |first13=Steven J. |last14=Scheffer |first14=Marten |last15=Winkelmann |first15=Ricarda |date=2018 |title=Trajectories of the Earth System in the Anthropocene |journal=Proceedings of the National Academy of Sciences |language=en |volume=115 |issue=33 |pages=8252–8259 |doi=10.1073/pnas.1810141115 |issn=0027-8424 |pmc=6099852 |pmid=30082409 |doi-access=free |bibcode=2018PNAS..115.8252S }}</ref>  identifies nine stressors of planetary support systems that need to stay within critical limits to preserve stable and safe biospheric conditions (see figure below). Climate change and biodiversity loss are seen as especially crucial, since on their own, they could push the Earth system out of the Holocene state: “transitions between time periods in Earth history have often been delineated by substantial shifts in climate, the biosphere, or both.” <ref name=":4" />  
[[File:Estimates_of_how_the_different_control_variables_for_seven_of_nine_planetary_boundaries_have_changed_from_1950_to_present.png|thumb|Estimates of how the different control variables for seven of nine planetary boundaries have changed from 1950 to present. The green shaded polygon represents the safe operating space.]]
The scientific consensus is that humanity has exceeded three to five of the nine planetary boundaries for safe use of the biosphere and is pressing hard on several more.<ref name=":5" /> By itself, crossing one of the planetary boundaries does not prove humanity has exceeded Earth's human carrying capacity; perhaps technological improvements or clever management might reduce this stressor and bring us back within the biosphere's safe operating space. But when several boundaries are crossed, it becomes harder to argue that carrying capacity has not been breached.<ref>{{Cite journal |last=Higgs |first=Kerryn |date=2017 |title=Limits to growth: human economy and planetary boundaries |journal=[[The Journal of Population and Sustainability]] |volume=2 |issue=1 |doi=10.3197/jps.2017.2.1.15 |issn=2398-5496|doi-access=free }}</ref> 

Because fewer people helps reduce all nine planetary stressors, the more boundaries are crossed, the clearer it appears that reducing human numbers is part of what is needed to get back within a safe operating space.<ref>{{Cite book |last=Coole |first=Diana H. |title=Should we control world population ? |date=2018 |publisher=Polity press |isbn=978-1-5095-2340-5 |series=Political theory today |location=Cambridge, UK Medford, MA}}</ref><ref>{{Cite book |last=Conly |first=Sarah |url=http://dx.doi.org/10.1093/acprof:oso/9780190203436.001.0001 |title=One Child |date=2016 |publisher=Oxford University Press |doi=10.1093/acprof:oso/9780190203436.001.0001 |isbn=978-0-19-020343-6}}</ref> Population growth regularly tops the list of causes of humanity's increasing impact on the natural environment in Earth system science literature.<ref>{{Cite journal |last=Bourban |first=Michel |date=2019 |title=Croissance démographique et changement climatique: repenser nos politiques dans le cadre des limites planétaires |url=http://dx.doi.org/10.3917/lpe.003.0019 |journal=La Pensée écologique |volume=3 |issue=1 |pages=19–37 |doi=10.3917/lpe.003.0019 |s2cid=203184072 |issn=2558-1465}}</ref> Recently, planetary boundaries developer Will Steffen and co-authors ranked global population change as the leading indicator of the influence of socio-economic trends on the functioning of the Earth system in the modern era, post-1750.<ref>{{Cite journal |last1=Steffen |first1=Will |last2=Broadgate |first2=Wendy |last3=Deutsch |first3=Lisa |last4=Gaffney |first4=Owen |last5=Ludwig |first5=Cornelia |date=2015 |title=The trajectory of the Anthropocene: The Great Acceleration |url=http://dx.doi.org/10.1177/2053019614564785 |journal=The Anthropocene Review |volume=2 |issue=1 |pages=84 |doi=10.1177/2053019614564785 |bibcode=2015AntRv...2...81S |issn=2053-0196|hdl=1885/66463 |s2cid=131524600 |hdl-access=free }}</ref>